Current approaches for monitoring safe operations and providing warnings of unsafe circumstances in an area, such as an at-grade railroad crossing, where different types of vehicles may operate generally fall into two categories. The first category attempts to exclude vehicles and persons from the grade crossing when a train is or may soon be passing through the crossing. These include simple “crossbuck” signage warning pedestrians and motorists that they are approaching an at-grade railroad crossing, warning lights and bells, and large gates which lower at the approach of a train and raise only after the train has passed.
These approaches are at best only partially successful. One problem is failure of the mechanical and/or electrical systems on occasion, which results in the system giving no warning or activating far too late for any human being to react properly in time. Additionally, human operators often deliberately and systematically evade or ignore the warning systems, either due to inattention, hurry, misjudgment as to the speed of the train and how quickly the tracks can be crossed, and/or the like. There are numerous cases in which a car or truck has been deliberately driven around fully lowered gates and been struck by the train as it attempts to cross the tracks.
Other approaches seek to detect unwanted and dangerous intrusions into the crossing region and signal alerts to appropriate groups or individuals. Besides the intruding vehicle/person themselves, other possible notification targets are the railroad dispatch office, local first responders, and the train operator through an in-locomotive notification system. These approaches generally include intrusive and non-intrusive sensor systems. Intrusive sensors require embedment into the pavement within the crossing. Such devices typically incur periodic failures due to shifting pavement, freeze/thaw cycles, and vehicle loading effects (e.g., heavy trucks). Sensors in this category include inductive loop detectors and magnetic sensors, and depend on the interaction between large metal objects and the electric field produced by the sensor or perturbation of the ambient magnetic field. As such, devices in this class cannot detect humans or any non-metallic objects, and generally cannot detect small metal objects, such as a bicycle or a wheelchair.
Non-intrusive sensors operate in a non-contact manner from a distance that is dependent on the sensor technology, typically measured in feet or tens of feet. Non-intrusive sensors can be further divided into imaging devices and non-imaging devices. Imaging devices, such as a camera, produce a representation of the object detected in the railroad crossing, which can be used by a human to further evaluate the nature of the object and decide a course of action. Non-imaging devices are merely presence detectors that give an indication something is present, and possibly its size. Examples of non-intrusive sensors include: radars (imaging and non-imaging, Doppler and presence sensing); active and passive acoustic and ultrasonic sensors; laser imaging detection and ranging (LIDAR); imaging and non-imaging long wave infrared (LWIR); and visible spectrum video imaging.
Non-imaging systems tend to be subject to high false alarm rates and poor spatial resolution. Visible spectrum imaging systems can be subject to high false alarm rates due to object effects (moving shadows, wind effects, reflections, glint, glare, coloration effects) and do not operate in fog/smoke/fine drizzle due to the scattering of light by the very small particles. Radar imaging systems have poor resolution and difficulty separating objects from background. LWIR systems depend on temperature differential and are of generally lower resolution than visible light systems. These systems operate well in darkness and smoke and fog, but are subject to glare, glint, and background confusion, as are visible spectrum systems. LIDAR (effectively light-based radar) actively scans an area with laser beams, which poses various safety concerns and requires an active scanning system, as does radar, which can break down.
An ultimate approach is to physically separate the crossing, either building a bridge for the train to cross over the road, or a bridge or tunnel for the road to cross over/under the tracks. However, this approach is an extremely expensive and time-consuming process, which is not practical in the vast majority of situations. For example, separating an at-grade crossing in this fashion costs several million dollars per crossing, and there are over 260,000 grade crossings in the United States.